Abstract
Mercury's geological history has been dominated by global contraction caused by secular cooling of the planet's interior. This cooling has had a profound effect on the expression of the planet's volcanism and tectonism, and the expressions of these two surface evolutionary processes are deeply intertwined. Here, we use case studies from the Hokusai quadrangle of Mercury to gain insight into the interplay between Mercury's volcanism and tectonism, which we review throughout this paper. We perform the first crater size–frequency analysis of the southernmost extent of Borealis Planitia, Mercury's largest expanse of volcanic plains, and find that it formed ~3.8–3.7 Ga. We discuss the importance of “intermediate plains”, a widespread unit in the Hokusai quadrangle, as the manifestation of relatively low-volume effusions with an uncertain stratigraphic relationship with Borealis Planitia. Finally, we detail the formation of the Suge Facula pitted ground during the geological history of Rachmaninoff crater, and hypothesise that such textures probably formed more widely on Mercury but have often either been buried by thick lava flows or otherwise obscured. Unanswered questions in this work can be used to drive the next phase of Mercury exploration and research with the arrival of the BepiColombo mission.
Highlights
Results from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission provided many answers about the history of volcanism on the Solar System's innermost planet, yet many questions remain
Small-volume effusive volcanism occurred sporadically in impact craters (Prockter et al, 2010; Blair et al, 2013; Fegan et al, 2017; Wright et al, 2018) for an uncertain duration following the cessation of large-volume eruptions
While large-volume effusive volcanism was coming to an end, the largest thrust-fault-related landforms formed in response to Mercury's global contraction (Byrne et al, 2014; Banks et al, 2015; Giacomini et al, 2020)
Summary
Results from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission provided many answers about the history of volcanism on the Solar System's innermost planet, yet many questions remain. With the launch of the BepiColombo mission (Benkhoff et al, 2010; Rothery et al, 2020a), set to return data from Mercury from 2026, we are in an appropriate interval to review our understanding of the planet's volcanism, which is strongly tied to its global tectonic regime. We illustrate the interplay between tectonism and volcanism on Mercury with case studies from the planet's Hokusai quadrangle (H05: Fig. 1: Wright et al, 2019), which encapsulates many aspects of the key constituent processes. For ease of comparison with Wright et al (2019), in which the geological mapping of the quadrangle was presented, here we show several figures of the whole or parts of H05 in the same Lambert Conformal Conic (LCC) projection (central meridian, 45°E; standard parallels, 30°N and 58°N), which we refer to as the “default” LCC projection of H05
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